The present invention relates to geometrical instruments of the type used to measure the inside dimension of a hole or aperture.
Inside dimension measuring guages of this general class are known in the prior art in which a dial indicator is attached to one end of a tubular body and a spindle installed within the body is caused to push on the contact plunger of the dial indicator. The other end of the tubular body is provided with a measuring contact which moves with the spindle but in a direction normal thereto. Examples of the prior art are to be found in German Pat. No. 437,754, British Pat. No. 1,319,748 and German Offenlegungshrift No. 1,623,311. Other examples of the prior art may be found in the classified collection of art in the U.S. Patent and Trademark Office in Class 33/Subclass 178.
In the guages of the prior art, the spindle has heretofore been provided with a lever for causing an axial displacement of the spindle in response to the manual manipulation of the lever. The function of the lever was to permit insertion of the measuring contact into the hole or orifice of an object for measurement of its inside dimension. The conventional practice for this purpose is to have a single lever pivoted to the tubular body, the lever including a slit on a working surface of the lever. A pin of the spindle engaged into the slit in such a fashion that rotation of the lever directly caused the spindle to be axially displaced.
The prior art inside dimension gauges suffered from a functional deficiency in that the posture of the tubular body was almost inevitably disturbed during the sequence required during the measuring operating, thereby causing the tubular body to lean to one side or another and thus giving inaccurate results. That is, when the measuring contacts were initially withdrawn toward the tubular body by the gripping of the operational lever and the guage then inserted into the hole or orifice of the object sought to be measured, the non-symmetric release of the lever providing for the measuring contacts to protrude outward toward the inside wall of the hole or orifice caused the undesirable displacement.
Since the lever and spindle of the prior art were directly linked, the lever itself had to be made very long if the spindle displacement was to be larger than the lever rotation and consequently this reduced the workability of the mechanism as a whole. Further, the connection by means of slit and pin between the lever and the spindle naturally limited the amount of reduction of the frictional resistance which coule be achieved. Thus, the prior art lever system required a strong force, which together with the presence of only a single lever resulted inevitably in a disturbed posture of the guage upon release of the lever.
Thus, the primary object of the present invention is to assure stable measurement of the inside dimension of a hole or orifice by using two levers situated such that their movement, transmitted over a linkage, displaces the spindle without disturbing the placement of the guage. Another object of the present invention is to make it possible to displace the spindle with a very small force through the use of a lever and link mechanism and thus permit optimum control of the posture of the guage when the lever is released.